Question

The HIV virus targets which CD receptor on immune cells?

• A. CD8
• B. CD4
• C. CD3
• D. CD20

Hint:

Recall which surface glycoprotein on CD4+ helper T cells is bound by HIV envelope protein gp120 to initiate infection.

Answer 1

The Correct Option is B

Step 1: HIV structure and tropism. HIV-1 is a lentivirus (retrovirus family) with a single-stranded, positive-sense RNA genome enclosed in an enveloped capsid. The envelope glycoprotein gp120 is the viral surface protein responsible for host cell recognition.

Step 2: CD4 as the primary receptor. gp120 binds with high affinity to CD4, a glycoprotein expressed on:
- CD4+ T helper lymphocytes (primary target)
- Monocytes and macrophages
- Dendritic cells
CD4 acts as the primary receptor; binding causes conformational change in gp120.

Step 3: Co-receptors (CCR5 and CXCR4). After gp120 binds CD4, it exposes the V3 loop and binds a co-receptor:
- CCR5: used by M-tropic (macrophage-tropic, R5) strains -- predominant in early infection
- CXCR4: used by T-tropic (T-lymphocyte-tropic, X4) strains -- associated with late-stage disease
The CCR5 deletion mutation (Delta32 homozygous) confers near-complete resistance to HIV.

Step 4: Consequences of CD4 depletion. Progressive destruction of CD4+ T cells leads to immunodeficiency. AIDS is defined as CD4 count < 200 cells/microlitre or the presence of an AIDS-defining illness.

Step 5: Exclusion of other options. CD8 is on cytotoxic T cells (involved in killing HIV-infected cells, not the target). CD3 is the T cell receptor complex. CD20 is on B cells (targeted by rituximab in lymphoma therapy).

Conclusion: HIV targets CD4 receptors as the primary entry receptor on immune cells.